how does fossil forms?-2022
Fossil
A fossil is
the mark or hardened remains of a plant or animal that lived thousands or
millions of years ago. Some fossils are leaves, shells or skeletons that were
preserved after a plant or animal passed away. Most of them are found in
sedimentary rocks. Animal fossils range from tiny microscopic to gigantic
dinosaur bone in size.
Identification
of fossils
Different types of fossils can be identified by comparing the
different shapes and parts of organs. Some methods of identification of fossil
are mentioned below.
1.
A part of the skeletal system or
the whole skeleton preserved in sedimentary rocks is a fossil.
2.
A fossil may be in the form of
molds and casts.
3.
Shells of animals, wood of plants,
etc. also may be preserved in sedimentary rocks as fossils.
Process of fossil formation
The process
of forming fossils is called fossilization. Any organism after its death may or
may not be fossilized. However, under favourable conditions, the organisms
which are composed of completely soft parts may be
fossilized. For instance, jellyfish have been wholly preserved. On the other
hand, even an organism with hard parts will not necessarily be fossilized. A
number of factors affect fossilization but the two factors given below play the
chief role in this process.
1.
If the animal has hard body parts,
the chance of fossilization increases.
2.
The organism must be covered by
protective materials shortly after the death. There are many ways of
fossilization; some of them are mentioned below:
· Some fossils are formed when animals are frozen in ice and preserved to the core.
- ·
Replacement of mineral instead of organic
material of the dead bodies in sediment gets petrified (turns into stone).
Fossilization occurs in this way as well.
Importance of
fossils
Fossils are very useful for the
following purposes:
1. They provide evidence of evolution of living beings.
2.
They help to know about the
extinct animals and plants.
3.
They show the
history of the location from where a fossil is obtained.
4.
Fossil fuels like coal and
petroleum are the main sources of energy.
5.
They help to make geological
timescale.
Fossil fuels
Fossil fuels
are non-renewable sources of energy. Coal, petroleum and natural gas are the
three categories of fossil fuels. Fossil fuels are formed from the dead bodies
of living beings after millions of years. At present, fossil fuels are being
widely used in industries, vehicles, kitchen, etc. as the main sources of energy.
Overuse of them brings energy crisis and pollution.
Coal
Coal is a black or brown
carbonaceous deposit formed by plant fossils. It is found in the form of thick
layer inside the earth and is taken out by mining. Its main components are
cellulose and lignin. Lignin forms from the wood of plants. Protein, oil,
organic acid and salts are also found in it. Especially, there are four types
of coal. The types of coal, hardness, colour and other properties are shown in
the following table.
|
S.NO. |
Types of Coal |
Colour |
Preselect fossils |
Hardness |
Weathering Property |
Other Properties |
|
1.
|
Lignite |
brown |
visible |
soft |
weathers easily |
burns with smoke, loosely held
particles |
|
2.
|
Sub-bituminous |
black |
visible |
slightly
hard |
weathers easily |
burns with
less flame, waxy |
|
3.
|
Bituminous |
black |
visible
under microscope |
hard |
Doesnot weather easily |
burns
with blue flame |
|
4.
|
Anthracite |
black
and shiny |
visible
under microscope |
hard |
does
not weather easily |
brittle,
burns without smoke |
Out of them, lignite is the worst and anthracite
is the best type of coal.
Formation of
coal
The exact mechanism of formation of coal is not known, but on the
basis of geological evidence, it is considered that it was formed from the
fossils of plants. In carboniferous period [345-280 million years ago], forest
of coal plants (fast growing bushes and giant tree ferns) grew in the swamp of
the earth. When they died and fell into quite swamp water, they were protected
against rotting. Bacteria and geothermal energy changed some parts of the wood
into gases that escaped out; the remaining black mixture containing mostly
carbon was left that became a coal seam
(Coal layer). In course of time, the increasing pressure from the overlying mud
and sand squeezed out most of the liquid, leaving behind a pasty mass which
slowly hardened into coal. In this way, coal was formed inside the earth. The
layer of coal inside the earth may vary from some inches to several feet.
Importance of coal
Coal is used for the following
purposes:
1.
It is used in industries, houses
and other places for heating and generating electricity.
2.
Coal tar obtained from coal is
used in the manufacture of plastic.
3.
Coal is used as fuel in steam
engines to change water into steam.
4. In some countries, coal is the main source of national economy.
5. It is used for manufacturing petroleum and synthetic natural gas.
Mineral oil
The word petroleum is derived from Latin word petr which means "rock" and oleum which means oil. So, it is rock oil. Oil and natural gas together are called petroleum. Paraffin, fuel, lubricating oil, kerosene, natural gases, grease, wax, asphalt and many other products are obtained from petroleum. Hydrocarbon covers 90-95% part of petroleum; the rest part is oxygen, sulphur, etc.
Formation of mineral oil
The
mechanism of the formation of mineral oil is open for speculation but
scientists believe that petroleum was formed from dead bodies of plants and
animals. As the plants and animals died, they piled up on the sea bottom. In
course of time, millions of tons of sand and mud covered them. Under pressure,
the mud and sand changed into rock. The formed rocks created a very high
pressure on the dead bodies. Because of high pressure at moderate temperature,
scarcity of oxygen, and by the action of bacteria, the dead bodies were
converted into a dark liquid trapped in the pore of the rocks, which was crude oil or petroleum. It takes millions of years to form crude oil. The
petroleum thus formed is stored between two impervious layers of the rocks. The
products obtained after the refining of crude oil and their uses are given
below:
S.No. |
Petroleum |
Uses |
1 |
Petroleum
ether |
Solvent,
cleaning |
2 |
Diesel |
Vehicles
fuel |
3 |
Kerosene |
Fuel |
4 |
Lubricating
oil, ease |
Lubrication |
5 |
Vaseline,
ease |
Medicine |
6 |
Paraffin
wax |
Manufacturing
of candle and matches |
7 |
Petroleum cake, bitumen Asphalt |
Fuel,
construction of road |
8 |
Petrol |
Fuel |
Importance of mineral oil
Some major uses of mineral oil are as the following:
- · It is used as a lubricant.
- · It is used as a fuel for cooking food.
- · It is used in vehicles as a fuel.
- · It is used in many industries as a fuel.
- · It is used in manufacturing of plastics, chemical fertilizers,
pesticides, paints, explosives, medicine, etc.
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